I was under the impression that what you're doing should work but after trying it out I can get the same behaviour. I'm wondering if in Central you have to delete the form and then reupload when changing the version I wasn't sure from reading the docs that that was right.
I'll share this post on the #central-codeslack channel and see if anyone has a good answer! Maybe the docs need to be updated to make this process clearer.
Thank you for verifying.
Indeed, by deleting the form, on can uploade a new version having the same formID.
However, you loose your submissions plus: in ODK Collect v1.26.1 one would NOT find the new version of the form for download. No matter if 'hide old versions' be ticked or not.